The air freezing technology was invented by Gorrie et al. 140 years ago, and the world's first ice making started then.
After that, the refrigeration efficiency has been improved by using coolants such as ammonia and chlorofluocarbon. However, due to the problem of global warming, the use of chlorofluocarbon, which has a high environmental problem index, has been inhibited.
Under these circumstances, the air freezing technology, which uses natural air for freezing, has been attracting attention again. Many of the expanders provided for such air freezing device employ a turbine. There have been other types of the expanders proposed, which form a cylinder piston member for cooling air from a piston, a crosshead, a connecting rod and a crank, which can reduce generation of heat by side thrust loss. Further, air refrigeration by means of the rotation-reciprocation conversion using a planetary gear has been developed.
The air refrigeration device employing the turbine-type expander has a compression-expansion ratio small as 2 to 3 and therefore need to be equipped with a plurality of turbines of two stages or three stages. With such a structure, the entire device is large, and is difficult to be made smaller. Further, such an expander entails drawbacks that it need to make the rotation constant at high speed and is difficult to adjust the temperature. Also, the turbine is easily damaged and expensive. Unless the rotation speed of the turbine is increased, the efficiency is low. At the same time, because of the high-speed rotation, the turbine is easily damaged. If one blade of a turbine is broken, other blades are always entangled and broken, easily making the damage worse.
Such an expander which employs a piston, a crosshead, a connecting rod and a crank becomes large, and is difficult to be made smaller or be multicylinder. Further, such an expander is operated at a low speed of about 300 rpm, and it is difficult to increase its speed. Further, the efficiency is low.
An expander which employs planetary gears has a large gear loss, and operates in one stage, which increases the size of the cylinder. Therefore, it is difficult to increase the volume. Further, the expander is difficult to be made into a multicylinder type or increase its speed. Instead of making a multicylinder reduction, usually, expanders of the same type are simultaneously operated, which increases the size and degrades the efficiency.